add: unit and integration testing

app/node_modules/escape-string-regexp/index.d.ts

@@ -0,0 +1,18 @@
+/**
+Escape RegExp special characters.
+
+You can also use this to escape a string that is inserted into the middle of a regex, for example, into a character class.
+
+@example
+```
+import escapeStringRegexp = require('escape-string-regexp');
+
+const escapedString = escapeStringRegexp('How much $ for a 🦄?');
+//=> 'How much \\$ for a 🦄\\?'
+
+new RegExp(escapedString);
+```
+*/
+declare const escapeStringRegexp: (string: string) => string;
+
+export = escapeStringRegexp;